Showing papers in "Surface & Coatings Technology in 1990"
AeA1
TL;DR: In this paper, the authors investigated the statistical nature of scratch failure by counting the number of individual failures at a given load for a fixed scratch length, and the results were analyzed in terms of the Weibull distribution.
Abstract: Both hardness testing and scratch adhesion testing are now routinely used for coating evaluation, although the fundamental understanding of both processes is somewhat limited. To establish the hardness of thin coatings independent of substrate, the volume-law-of-mixtures hardness model has been applied to a large number of coating/substrate systems, and extensions to an earlier model have been developed including better deforming volume calculations and the ability to obtain best-fit coating parameters. In order to extend the understanding of the scratch test, the statistical nature of coating failure has been investigated by counting the number of individual failures at a given load for a fixed scratch length. The results are analysed in terms of the Weibull distribution and these are related to the surface roughness of the substrate prior to coating. With increased surface roughness both the critical load and Weibull parameters are reduced, reflecting a change in the distribution of interfacial flaws.
259 citations
TL;DR: In this paper, ultra-hard (hardness greater than 4000 HV 005) coatings derived from TiB2 were investigated as thin, wear-protective coatings for cutting tools.
Abstract: Ultrahard (hardness greater than 4000 HV 005) coatings derived from TiB2 were investigated as thin, wear-protective coatings for cutting tools Deposition methods were based on non-reactive as well as reactive sputter deposition employing dc magnetron sputtering from TiB2 targets Coatings were deposited onto molybdenum, niobium and cemented carbide substrates Very fine-columned films with an (001)-oriented TiB2 phase are formed by means of non-reactive sputtering of TiB2 targets Coatings deposited reactively in Ar-N2-C3H8 atmospheres exhibit very fine-grained to fracture-amorphous structures In the case of reactive sputtering in Ar-N2 gas mixtures a hexagonal TiB2−xNy phase appears at low N2 flows An increase of the N2 flow results in the formation of an additional phase based on TiN Reactive deposition in Ar-C3H8 atmospheres leads to the existence of mixed-phase structures with phases based on TiB2 and TiC Quarternary films grown in Ar-N2-C3H8 mixtures show multiphase structures consisting of phases based on TiB2 as well as TiC and TiN Vickers microhardness measurements on coatings 3 - 5 μm thick on cemented carbide inserts gave the following maximum HV 005 values: Ti-B films 4000; Ti-B-N 4800; Ti-B-C 4000; Ti-B-C-N 4200 Stresses were found to be compressive with values up to 4 GPa The results of scratch tests indicate very good adherence Ti-B-coated cemented carbide inserts have been tested in the turning of aluminum alloys with promising results
150 citations
TL;DR: In this article, it has been shown that a specific number of single layers, around 100-200 for a total layer thickness of 5 μm, produces optimum characteristics with regard to crack propagation resistance and wear behaviour, especially under interrupted cutting conditions.
Abstract: Multilayer TiC/TiB2 coatings were prepared by magnetron sputtering with various degrees of ion bombardment during deposition. In previous studies, it has been shown that a specific number of single layers, around 100 – 200 for a total layer thickness of 5 μm, produces optimum characteristics with regard to crack propagation resistance and wear behaviour, especially under interrupted cutting conditions. These are indications showing that cracks are deflected at the interface zones. These zones have an extension of about 2 – 3 nm after sputter deposition without “biasing” the substrate. Ion bombardment during deposition leads to similar interface zones, to modifications in the coating texture, and to the best coating properties being achieved at a larger number of single layers. Optimum properties and wear resistance were found for 500 single layers in a coating thickness of 5 μm. Constitution, properties and wear behaviour are discussed as a function of the fabrication parameters.
125 citations
TL;DR: In this paper, a scratch test for in situ testing of coating adhesion in the scanning electron microscope has been designed, where scratch tests were performed on TiN-coated high speed steel substrates with various coating thicknesses and substrate hardnesses.
Abstract: A scratch test apparatus for in situ testing of coating adhesion in the scanning electron microscope has been designed. Scratch tests were performed on TiN-coated high speed steel substrates with various coating thicknesses and substrate hardnesses. Four groups of coating damage and detachment mechanisms were identified: deformation, crack formation, chip formation and flaking. In all cases, incipient coating failure was associated with a sharp increase in the friction force readings. The maximum normal force that the coating-substrate composite could sustain increased significantly with increasing coating thickness and substrate hardness. An interesting observation was that direct adhesive failure by interfacial fracture only occurred for the combination of a thick (3 μm) coating on a hard (1000 HV) substrate. In all other cases, coating failure was due to a ductile chip formation mechanism. The detailed influence of the coating thickness and substrate hardness on the resulting coating failure modes is illustrated in the paper by the introduction of coating failure maps. The results demonstrate the great potential for in situ studies in order to obtain a better understanding of the basic coating failure mechanisms. In situ scratching allows the dynamics of the process to be studied; the coating damage and detachment mechanisms in front of the tip can be identified and the scratching events can be directly correlated to the corresponding friction force characteristics. Unfortunately, direct extrapolation of results from the in situ test to the conventional scratch test is difficult owing to the smaller tip radius (25 instead of 200 μm) used in the in situ experiments.
112 citations
TL;DR: In this paper, the authors investigated the isothermal oxidation kinetics of Ni-35Cr-6Al-0.95Y, Ni-18Cr-12Al- 0.3Y, and Ni-16Cr-5Al-1Al 0.5Y bond coat alloys and examined the effect of these alloys on the thermal barrier coating cyclic life.
Abstract: The paper investigates the isothermal oxidation kinetics of Ni-35Cr-6Al-0.95Y, Ni-18Cr-12Al-0.3Y, and Ni-16Cr-6Al-0.3Y low-pressure plasma-sprayed bond coat alloys and examines the effect of these alloys on the thermal barrier coating (TBC) cyclic life. TBC life was examined by cycling substrates coated with the different bond coats and a ZrO2-7 wt pct Y2O3 TBC in an air-rich burner rig flame between 1150 C and room temperature. The oxidation kinetics of the three bond coat alloys was examined by isothermal oxidation of monolithic NJiCrAlY coupons at 1083 C. The Ni-35Cr-6Al-0.95Y alloy exhibits comparatively high isothermal oxidation weight gains and provides the longest TBC life, whereas the Ni-16Cr-6Al-0.3Y alloy had the lowest weight gains and provided the shortest TBC life. The results show that, although bond coat oxidation is known to have a strong detrimental effect on TBC life, it is not the only bond coat factor that determines TBC life.
100 citations
TL;DR: In this paper, the formation and self-lubrication mechanisms of boric acid films on boric oxide coatings prepared by vacuum evaporation were investigated, and a triclinic crystal structure was proposed for the mechanism of self lubrication.
Abstract: An investigation was made of the formation and self-lubrication mechanisms of boric acid films on boric oxide coatings prepared by vacuum evaporation. Measured friction coefficients of a steel ball sliding on a boric-oxide-coated steel disk and a sapphire ball sliding on a boric-oxide-coated alumina disk were 0.025–0.05 at steady state, depending on load and substrate material. This low friction was correlated with the formation of a lubricious boric acid film on boric oxide coatings exposed to open air. For the mechanism of self-lubrication, the layered triclinic crystal structure of boric acid was proposed. The atoms constituting each boric acid molecule are arrayed in closely packed and strongly bonded layers that are 0.318 nm apart and held together by weak forces, such as van der Waals'. It is hypothesized that, during sliding, these layers can align themselves parallel to the direction of relative motion and, once so aligned, can slide over one another with relative ease to provide low friction. Structural and chemical findings were included to substantiate the proposed solid lubrication mechanism.
96 citations
TL;DR: In this article, various post-deposition methods were studied in order to improve the corrosion resistance of TiN and ZrN coatings, including pulsing of nitrogen flow, rotation of the specimen and separate sputtering during deposition.
Abstract: TiN and ZrN coatings were deposited by reactive triode ion plating onto high-speed steel rods, and onto both rods and strips of austenitic stainless steel. Various methods were studied in order to improve the corrosion resistance of these coatings. They included the pulsing of nitrogen flow, the rotation of the specimen and separate sputtering during deposition. Different post-deposition methods were also studied. They included chemical passivation and annealing in vacuum. Corrosion tests were used to study the effectiveness of these methods. Cross-sectional scanning electron microscopy and Auger analysis were used to study the structure and morphology of the coatings. It was found that all of the methods studied improved the corrosion resistance of TiN and ZrN coatings.
93 citations
TL;DR: In this article, the authors investigated how and why TiN coatings modify the performance of high speed steel cutting tools and concluded that a unique combination of sufficient adhesion to the substrate, high hot hardness, high wear resistance and an ability to improve the contact conditions at the cutting edge is the answer.
Abstract: TiN coatings deposited onto high speed steel (HSS) by physical vapour deposition have successfully been used in metal cutting applications for a number of years Many papers have been presented which all show that TiN coatings often yield decreased wear rates and, usually, reduced friction coefficients Although different theories are proposed in the literature (hardness theory, diffusion barrier theory, thermal barrier theory, reduced friction theory etc), most papers have not dealt with the question of how and why TiN coatings modify the performance of HSS cutting tools The present paper contributes to the answer of this question by (1) organizing published information about significant mechanical and chemical properties of TiN and (2) closely discussing different proposed theories and making comparisons with results from the broad spectrum of experiments (tool wear simulation testing, scratch testing in a scanning electron microscope, particle erosion testing, chip formation studies, metal cutting etc) performed by the authors A unique combination of sufficient adhesion to the substrate, high hot hardness, high wear resistance and an ability to improve the contact conditions at the cutting edge is concluded to be the answer The complex interrelationships encompassed by this explanation are displayed in a flowchart The thermal barrier function and the relatively low sliding friction coefficient of TiN are believed to be of minor importance
91 citations
TL;DR: In this article, the performance of newly developed titanium carbonitride coatings in cutting and forming operations is discussed, specifically in comparison with titanium nitride, and it is shown that titanium carbonite is to be recommended when abrasion is the main wear mechanism, though it also has advantages in reducing adhesive wear.
Abstract: The performance of newly developed titanium carbonitride coatings in cutting and forming operations is discussed, specifically in comparison with titanium nitride. It is shown that titanium carbonitride is to be recommended when abrasion is the main wear mechanism, though it also has advantages in reducing adhesive wear. When interrupted cutting is encountered, titanium nitride coatinhs are shown to be preferable.
91 citations
TL;DR: In this paper, the principal current and new thermal spray coating processes used for compressor, combustion chamber and turbine applications in aero engines are described with particular reference to high velocity combustion and plasma spraying techniques.
Abstract: The principal current and new thermal spray coating processes used for compressor, combustion chamber and turbine applications in aero engines are described with particular reference to high velocity combustion and plasma spraying techniques. The uses of coatings for wear and erosion resistance, oxidation and corrosion control, thermal barrier applications and gas path sealing (clearance control) are discussed.
90 citations
TL;DR: In this paper, an opposed cathode sputtering system with the ability to coat parts with a size up to 15 cm in diameter and 30 cm in length was presented. But the results showed that the substrate bias current density was related to the magnetic field strength between the two opposed cathodes and to the sputtering pressure.
Abstract: Attention is given to an opposed cathode sputtering system constructed with the ability to coat parts with a size up to 15 cm in diameter and 30 cm in length. Initial trials with this system revealed very low substrate bias currents. When the AlNiCo magnets in the two opposed cathodes were arranged in a mirrored configuration, the plasma density at the substrate was low, and the substrate bias current density was less than 1 mA/sq cm. If the magnets were arranged in a closed-field configuration where the field lines from one set of magnets were coupled with the other set, the substrate bias current density was as high as 5.7 mA/sq cm when NdFeB magnets were used. In the closed-field configuration, the substrate bias current density was related to the magnetic field strength between the two cathodes and to the sputtering pressure. Hard well-adhered TiN coatings were reactively sputtered in the opposed cathode system in the closed-field configuration, but the mirrored configuration produced films with poor adhesion because of etching problems and low plasma density at the substrate.
TL;DR: In this article, the effect of oxygen incorporation within sputter-deposited MoS 2 solid lubricant films was studied using extended X-ray absorption fine structure (EXAFS), Xray photoelectron spectroscopy (XPS) and X-Ray diffraction (XRD).
Abstract: The morphology and crystallite structure/orientation of sputter-deposited MoS 2 solid lubricant films have been shown to be strongly affected by oxygen-containing species in the sputtering chamber. We have studied the effect of oxygen incorporation within these films using extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Films produced at The Aerospace Corporation, the National Centre of Tribology (U.K.), Hohman Plating and Manufacturing, and NASA Lewis Research Center were studied to determine common characteristics of different MoS 2 films produced by sputter deposition. In agreement with previous results, XPS of the films indicated a bulk anion:cation ratio ( i.e. (S+O):Mo) of about 2, and XRD revealed that the films consisted completely of MoS 2 -like phases that were compressed in the ( h k 0) directions as compared with pure MoS 2 . This “edge plane compression” appeared to correlate with oxygen content. EXAFS confirmed the absence of MoO 2 in the films and indicated that the films actually consist of two similar MoS 2 -like phases. Correlation of the EXAFS results with those obtained from XPS and XRD indicated that the two phases are MoS 2 and an MoS 2- x O x substitutional solution. The solid solution may be described as MoS 2 with oxygen atoms that have substituted for sulfur atoms in the MoS 2 crystal lattice. Relative peak height changes in the EXAFS radial distribution curves indicated that increasing amounts of oxygen cause a reduction in the size of crystallites in the films. The presence of the MoS 2- x O x phase may explain the superior tribological performance of MoS 2 films in some applications, which has been shown to correlate with oxygen impurities in the films.
TL;DR: In this paper, thin films of titanium nitride were prepared by the arc ion plating process and deposited onto polished WC-Co substrates to investigate macroparticles (MPs), morphology and surface roughness.
Abstract: In this study, thin films of titanium nitride were prepared by the arc ion plating process and deposited onto polished WC-Co substrates to investigate macroparticles (MPs), morphology and surface roughness. The deposition variables explored were arc current, deposition time, substrate distance, nitrogen pressure, substrate bias, target thickness and electromagnetic coil current of the target. The results show that the number of MPs and their area ration vary directly with arc current, deposition time and target thickness, inversely with substrate distance, substrate bias and nitrogen pressure. Positive relationships exist between the deposition rate and the number of MPs, and between the deposition rate and the surface roughness.
TL;DR: In this paper, a model including both primary and secondary cooling was developed to predict the effect of the substrate temperature on residual stress in thermally sprayed coatings, and the importance of primary cooling was confirmed.
Abstract: Post-fabrication cool down (secondary cooling) is said to be the major cause of the residual stress in thermally sprayed coatings. Primary cooling, the cooling of spray particles to substrate temperature after solidification, is seldom considered. The purpose of the present work is to demonstrate the importance of primary cooling. A model including both primary and secondary cooling was developed to predict the effect of the substrate temperature on residual stress. The following three sequential mechanisms were considered: (1) shrinkage of the spray particles after solidification; (2) deformation of the deposit during spraying; (3) deformation of the deposit after spraying. When the expansion coefficient of the coating is less than that of the substrate, the model predicts that a high substrate temperature induces compressive stress and that a low substrate temperature generates tensile stress. Therefore an optimum substrate temperature exists to minimize residual stress. The modelling results were confirmed by experiments. When the relation between expansion coefficients is reversed, the stress is always tensile throughout the spraying procedure. The present model explains the complicated behaviour of residual stress in sprayed coatings. The importance of primary cooling is confirmed.
TL;DR: In this paper, the authors investigated the relative corrosion protection provided on 304 stainless steel by various coating and pretreatment routes designed to isolate the substrate from the environment, including combinations of plasma oxidizing, plasma nitriding and chromium, nickel and titanium nitride coatings produced by triode ion plating methods.
Abstract: Potentiodynamic methods were used to investigate the relative corrosion protection provided on 304 stainless steel by various coating and pretreatment routes designed to isolate the substrate from the environment. These include combinations of plasma oxidizing, plasma nitriding and chromium, nickel and titanium nitride coatings produced by triode ion plating methods. It is shown that optimization of the layer structure and galvanic coupling are vital where a combination of wear and corrosion resistance is required. Nickel interlayers under TiN, for example, are shown to provide improved protection against corrosion. Attempts to increase corrosion resistance by producing a passive layer through a d.c. plasma processing stage on the substrate were not so successful, and the reasons for this are discussed.
TL;DR: In this article, the applicability of discharge enhancement to the plasma nitriding process is examined in terms of surface layer growth rate, hardness profiles and coverage uniformity, and a correlation of visual and optical emission spectroscopy analyses of practical discharges with predictive equations for plasma phenomena can be useful in explaining observed discharge effects.
Abstract: Increasing industrial interest in the use of enhanced low pressure ion plating techniques for surface coating applications led the authors to examine the applicability of discharge enhancement to the plasma nitriding process. The performance of various d.c. diode, triode and r.f. systems is discussed in terms of surface layer growth rate, hardness profiles and coverage uniformity. It is shown that a correlation of visual and optical emission spectroscopy analyses of practical discharges with predictive equations for plasma phenomena can be useful in explaining observed discharge effects, thus assisting development and optimization of the plasma nitriding process.
TL;DR: In this article, a cubic boron nitride (c-BN) was synthesized by the activated reactive evaporation process using a hot cathode plasma discharge in a parallel magnetic field around the substrate.
Abstract: A method of synthesizing cubic boron nitride (c-BN) films by the activated reactive evaporation process was investigated. A special feature of the gas activation process is that a hot cathode plasma discharge in a parallel magnetic field is used. A conventional type of ion plating apparatus, with an electron beam gun for the evaporation of boron, was used to synthesize c-BN films on a single-crystal silicon plate. A stoichiometric boron nitride film was obtained by reacting boron vapour with high density nitrogen ions, prepared using a hot cathode plasma discharge in a parallel magnetic field around the substrate. Argon gas was mixed with the reactant nitrogen gas to enhance BN formation. An r.f. bias potential was applied to the substrate in order to obtain the cubic BN phase. The optimum value of the total gas pressure in the evaporation chamber was in the range 2.6 × 10 -2 -1.1 × 10 -1 Pa. The structures of the films obtained were characterized using IR absorption spectroscopy and X-ray diffraction analysis.
TL;DR: In this article, the transition from porous, soft TiN films with a zone I microstructure to compact, hard hard, gold-coated, high-quality high-density TiN film was investigated at a substrate bias U s of about -40 V.
Abstract: Ion bombardment of growing films is one of the possible ways to produce films with specific properties. As yet there are no general rules for the production of these films. The quality of TiN films produced depends on the deposition conditions. A sharp transition from porous, black TiN films to compact, dense, bright gold TiN films is observed at a substrate bias U s of about -40 V. Recent experiments have indicated that the microstructure of TiN films and the transition mentioned above can be controlled by the ion energy delivered to the growing film per deposited particle E p = eU s v i / v m . This paper investigates the transition from porous, soft TiN films with a zone I microstructure to compact, hard TiN films with a zone T microstructure as a function of i s , U s and the deposition rate a D at constant temperature T s = 350 °C and pressure p T = 5 Pa. Correlations between the microhardness HV, the macrostress σ, the microstrain e , the lattice parameters, the intensities of the X-ray reflections and the colour and appearance of the film are discussed. The zone I to zone T transition is observed at E p ≈ 150 eV atom -1 .
TL;DR: In this paper, the effect of a modified AIP source, characterized by the presence of a magnetic field on the plasma stream, has been investigated, and the surface properties of TiN films were examined by varying the magnetic field strength and the pressure of nitrogen; quantitative measurements were made using an image analyser.
Abstract: Preparation of films using the arc ion plating (AIP) process encounters a significant problem in that macroparticles are produced. To overcome this problem, the effect of a modified AIP source, characterized by the presence of a magnetic field on the plasma stream, has been investigated. The surface properties of TiN films were examined by varying the magnetic field strength and the pressure of nitrogen; quantitative measurements were made using an image analyser. It was found that the number of macroparticles could be reduced to 10% of that of the conventional process and that a high deposition rate, similar to that of the conventional process, could be achieved.
TL;DR: In this paper, new homogeneous and metastable films within the Ti-B-C-N system were prepared by magnetron sputter ion plating using a TiB2 target in the d.c. mode.
Abstract: In order to advance the development of extremely hard coatings, new homogeneous and metastable films within the Ti-B-C-N system were prepared by magnetron sputter ion plating using a TiB2 target in the d.c. mode. Multicomponent layers of different compositions and structures were deposited by varying the reactive gases methane (CH4) and nitrogen (N2) and the dominant process parameters (e.g. sputtering power and substrate bias). X-ray diffraction studies of the coatings revealed either an amorphous structure or crystallization in a hexagonal lattice. The lattice parameters were strongly influenced by the quantity of carbon and nitrogen incorporated. Electron microprobe analysis was used to determine the coating compositions. Evaluation of the characteristic light element X-ray spectra provided initial qualitative data on chemical bonding properties. Auger electron spectroscopy confirmed the construction of the films. The Palmquist method and hertzian indentations were used to characterize film toughness. The remaining mechanical coating properties were investigated by means of microhardness measurements and the CSEM scratch test. Scanning electron microscopy indicated an extremely dense coating structure. Superhardness up to values of 7000 HV 0.05 was the dominant property. Coating thicknesses ranging from 6 to 25 μm were realized. Behaviour of the Ti-B-C-N layers in abrasive wear tests was favourable.
TL;DR: In this article, the phase composition and texture of physically vapour deposited films are taken into account to determine the hardness, adhesion and tribological behaviour of these films (under both abrasive and adhesive wear conditions) have been determined and related to microstructure and phase composition.
Abstract: It is now well established that the microstructure of physically vapour deposited films dictates many of their mechanical properties which in turn determine the tribological performance of the film. In particular phase composition and texture need to be taken into consideration if the properties of a film are to be fully understood. By controlling the partial pressure of nitrogen during reactive sputtering it has been possible to produce films of compositions ranging from pure chromium to CrN. At low nitrogen partial pressures the films contained a mixture of Cr2N and CrN phases, but with increasing nitrogen partial pressure the CrN phase became dominant and exhibited a change in texture from {200} to {111}. The hardness, adhesion and tribological behaviour of these films (under both abrasive and adhesive wear conditions) have been determined and related to microstructure and phase composition. Under similar deposition conditions of pressure, coating time and substrate bias voltage, the hardest films consist of {200}-textured CrN, an effect attributed to the lower density of the films containing a mixture of Cr2N-CrN. Best abrasive wear properties are obtained for the hardest films, but the results of sphere-on-disc wear tests show that optimum sliding wear behaviour occurs for the smoothest of the {200}-textured CrN films.
TL;DR: Abrasive wear tests have been performed on sputtered TiN coatings on stainless steel with a range of titanium interlayer thicknesses, and the best wear properties are obtained for the thickest interlayer due to the increased interface toughness in this system as mentioned in this paper.
Abstract: The use of physically vapour-deposited TiN coatings for tribological applications is now commonplace, though the reasons for the improvements in wear behaviour they produce are not fully understood. In order to promote good adhesion between substrate and coating a thin titanium interlayer is often used. The presence of this interlayer in the case of sputtered coatings, or the presence of any unreacted titanium in the case of arcevaporated coatings, can have significant effects on the abrasive wear resistance of a coated component. Abrasive wear tests have been performed on sputtered TiN coatings on stainless steel with a range of titanium interlayer thicknesses. Best wear properties are obtained for the thickest interlayer due to the increased interface toughness in this system. Arc-evaporated coatings perform better than similar sputtered coatings under mild abrasive conditions, but the behaviour is reversed for more severe abrasive conditions. A model is proposed to account for these observations, but clearly the presence of titanium can have both advantages and disadvantages for the production of abrasion resistant coatings by physical vapour decompositon techniques.
TL;DR: A number of plasma-sprayed yttria-stabilized zirconia coatings were prepared representing a combination of significantly different starting powders and different plasma torch designs as mentioned in this paper.
Abstract: A number of plasma-sprayed yttria-stabilized zirconia coatings were prepared representing a combination of significantly different starting powders and different plasma torch designs. The coatings had densities in the range 85%–91% of the theoretical. Coating hardness, particle erosion resistance and cohesive strength were proportional to density. The thermal fatigue resistance of zirconia coatings, 1.3 mm (0.05 in) thick, increased with increasing density, but their thermal insulation value was inversely proportional to density. In general, the coatings exhibited a number of properties related to density without separate regard to process.
TL;DR: In this paper, sintered tungsten carbide (WC) without cobalt metal was used as the substrate and the effect of surface decarburization of the substrate to improve the adhesion strength of diamond films was investigated.
Abstract: One of the expected applications of diamond coatings is in cutting tools for non-ferrous metals and alloys such as Al-Si and non-metals such as hard carbons etc. However, the poor adhesion strength of diamond films must be improved for practical use in cutting. In this study, sintered tungsten carbide (WC) without cobalt metal was used as the substrate and the effect of surface decarburization of the substrate to improve the adhesion strength of diamond films was investigated. Surface decarburization and diamond coating were carried out using a microwave plasma chemical vapour deposition apparatus. Good adhesion was obtained by surface decarburization of the substrate before diamond coating. From the results of observations by scanning electron microscopy and transmission electron microscopy, the improvement in the adhesion strength can be considered to be due to an increase in the contact area between the film and the substrate by generation of fine WC grains on the surface of the substrate, with the film embedded in the shape of a wedge at the fine WC grain boundaries. The coated insert demonstrates a very small steady wear without film flaking when milling a hard carbon compared with the large amount of wear exhibited by uncoated cemented carbides.
TL;DR: In this article, the authors describe the synergistic effect of corrosion and wear of iron sliding on sapphire in sulfuric acid, and the effect of surface films on the wear and friction of plasma-deposited diamond-like carbon (amorphous hydrogenated carbon) films in sliding contact with silicon nitride.
Abstract: Mechanochemical interaction studies can contribute to the understanding of wear and friction of materials. Specific examples of experimental results relative to the subject are discussed. There are two parts: one describes the synergistic effect of corrosion and wear of iron sliding on sapphire in sulfuric acid, and the other describes the effect of surface films on the wear and friction of plasma-deposited diamondlike carbon (amorphous hydrogenated carbon) films in sliding contact with silicon nitride. The concentration of acid (pH) is an important factor in controlling the iron loss caused by wear-corrosion processes in sulfuric acid. The mechanical action can cause chemical reactions to proceed much faster than they would otherwise. The diamondlike carbon (DLC) films are shown to behave tribologically much like bulk diamond. In a dry nitrogen environment, a mechanochemical reaction produces a substance which greatly decreases the coefficient of friction. In a moist air environment, mechanochemical interactions drastically reduce the wear life of DLC films and water vapor greatly increases friction.
TL;DR: In this paper, a pin-on-disc apparatus was used to determine the friction coefficient in dry air or nitrogen under a hertzian pressure of about 1 GPa at a speed of 10 mm s -1.
Abstract: Dense and thick MoS x coatings were prepared by d.c. reactive magnetron sputtering of a molybdenum target in an argon and H 2 S atmosphere onto stainless steel substrates polished to different roughnesses. The deposition rate was 0.3-0.5 μm min -1 and the thickness ranged from 0.7 to 28 μm. Composition, morphology, hardness, crystallographic structure and tribological properties of MoS x coatings were investigated with respect to the deposition parameters (pressure, temperature, substrate bias, gas flow). The hexagonal structure was observed for MoS x layers with x ranging from 1.3 to 2.1. A pin-on-disc apparatus was used to determine the friction coefficient in dry air or nitrogen under a hertzian pressure of about 1 GPa at a speed of 10 mm s -1 . These tests revealed a minimum friction coefficient of 0.025 for hexagonal structure and (001)-textured films between MoS 1.5 and MoS 1.7 with hardness values of 6000 MPa and 4000 MPa respectively (Knoop device) and a thickness of 1 - 4 μm.
TL;DR: In this paper, a survey and a classification of the most common projective layer materials are given and typical examples of coating concepts with improved properties are discussed, including microstructure, properties and application behavior.
Abstract: Improved knowledge of the ways in which the structures, properties and behaviour of coated materials are interrelated as well as technical advances in the production of specific layers constitute a basis on which a better understanding of application characteristics and an application-oriented material selection become possible. Many of the relations between constitution, microstructure, properties and application behaviour developed for bulk materials can also be used to understand the behaviour of layer materials and to optimize coatings. A survey and a classification of the most common projective layer materials are given and typical examples of coating concepts with improved properties are discussed.
TL;DR: In this paper, the sliding friction coefficient of a sphere-on-disc test was found to be approximately constant except for the case where coated spheres slide on coated flats, and the amount of sphere and disc wear decreases with substrate bias, though the wear rate for the disc increases at the very highest bias voltages.
Abstract: Although the mechanisms by which titanium nitride (TiN) coatings can affect the abrasive wear resistance of coated components are well documented, relatively little is known about the sliding wear behaviour of these materials. Sphere-on-disc tests have been performed on sputtered TiN coatings, deposited at a range of bias voltages, using both coated and uncoated spheres. The amount of sphere and disc wear decreases with substrate bias, though the wear rate for the disc increases at the very highest bias voltages. The coefficient of sliding friction is approximately constant except for the case where coated spheres slide on coated flats. The mechanisms of adhesive wear are based on the local transfer of iron, which subsequently becomes trapped in the open regions within the coating microstructure, increasing the sphere-coating adhesion at these positions. Consequently, best sliding wear properties result from hard, dense coatings as produced at high substrate bias voltages, although oxidative wear becomes increasingly important as the bias is increased.
TL;DR: In this paper, a range of thermal spraying processes available for the deposition of surface coatings for compressor, combustion chamber and turbine section components in aero engines are described, and typical coating applications discussed.
Abstract: The range of thermal spraying processes available for the deposition of surface coatings for compressor, combustion chamber and turbine section components in aero engines are described, and typical coating applications discussed. Combustion flame, arc wire, high velocity combustion and plasma spraying techniques are described, and coatings for wear, oxidation and corrosion resistance, clearance control and thermal barrier applications are discussed.
TL;DR: In this paper, the advantages and current limitations of thin film systems in tribological situations are discussed, and a short review of the relevant basic concepts of friction and wear, of those elements of contact mechanics which are a necessary introduction to an understanding of tribological behaviour, and the stresses occurring at uncoated surfaces, initially under normal load only and then under combined normal and tangential loads.
Abstract: This paper aims to explain both the advantages and the current limitations of thin film systems in tribological situations. It begins with short reviews of the relevant basic concepts of friction and wear, of those elements of contact mechanics which are a necessary introduction to an understanding of tribological behaviour, and of the stresses occurring at uncoated surfaces, initially under normal load only and then under combined normal and tangential loads. It then describes the mechanics underlying the two technologically important systems of hard surfaces covered by soft coatings and relatively soft surfaces covered by hard coatings. The mechanics of the scratch test are then discussed and explanations are offered for the various failure modes observed during such a test. Finally, outlines are given of current and future programmes of work designed to elucidate the factors limiting coating performance.